The present invention relates to flame retardant halogen-free aromatic polycarbonates compositions utilizing an effective amount of a silicate resin as a flame retardant for a polycarbonate resin, where the silicate resin has condensed triorganosiloxy units, such as trimethylsiloxy units, and condensed diorganosiloxy units, such as methylvinylsiloxy units.
Prior to the present invention as shown, for example, by Bialous, et al, U.S. Pat. No. 3,971,756, or Mark et al, U.S. Pat. No. 4,110,299, various organic metal salts, or inorganic halides were utilized in combination with organosiloxanes to improve the flame retardant properties of polycarbonates. Certain organosilicon materials, such as organosilanes also were employed as plasticizers with polycarbonates as shown by Mark et al, U.S. Pat. No. 4,230,611.
In copending application of Policastro et al, Ser. No. 07/319,026, now U.S. Pat. No. 4,916,194 several poly(arylene silicon materials, such as aromatic polyestersiloxanes, or aromatic polyimidesiloxanes were found to be useful flame retardants for aromatic polycarbonates when used in effective amounts. However, the intermediates used in making such poly(arylsilicon) materials are not commercially available.
As used hereinafter, the term "flame retardance" or "nonflammable" or "flame resistance" with respect to the flame retardant polycarbonate compositions of the present invention means that the flame retardant polycarbonates can satisfy the UL94 V-0 requirements for flammability, as shown by the "Flammability of Plastic Materials Bulletin" of Jan. 24, 1980. More particularly, a 5".times.1/2".times.1/16" polycarbonate test bar containing an effective amount,of the flame retardant is suspended vertically over a 3/4" Bunsen Burner flame as provided in the aforementioned UL94 test. The test sample preferably exhibits a UL94 V-0 rating which includes the following criteria:
A. Not have any specimen which burns with flaming combustion for more than 10 seconds after application of the test flame. PA1 B. Not have a total flaming combustion time exceeding 50 seconds for 10 flame applications for each set of five specimens. PA1 C. Not have any specimens which burn with flaming or glowing combustion up to the holding clamp. PA1 D. Not have any specimens which drip flaming particles that ignite dry absorbent surgical cotton located 12 inches (305 mm) below the test specimen. PA1 E. Not have any specimens with glowing combustion which persists for more than 30 seconds after the second removal of the test flame. PA1 (A) an aromatic polycarbonate resin, and PA1 (B) an effective amount of a silicate resin having from 1 to 2 moles of condensed triorganosiloxy units selected from trimethylsiloxy and dimethylphenylsiloxy units, and from 0.15 mole to 1 mole of condensed diorganosiloxy units selected from the class consisting of methylvinylsiloxy units, divinylsiloxy units and dimethylsiloxy units, per mole of SiO.sub.2 units
Although flame retardant aromatic polycarbonate compositions have been made using various materials, such as organic alkaline metal salts, siloxanes, inorganic halides, or certain polyarlylene silicon materials, it would be desirable to employ halogen-free material as flame retardants which can be made from readily available materials and which provide a V-0 UL-94 rating when blended with polycarbonates. In addition, it is often difficult to make flame retardant polycarbonate capable of satisfying the UL-94 V-0 test requirements at 1/16" which can be of potential importance in certain applications, such as business machine housings.
In addition to the UL94 test as shown above, fabricators of materials used in aircraft and sky-scrapers, often require that the materials emit low smoke and heat when burning. E.E. Smith, Fire Technology 8 (1972) 237 describes the Ohio State University Test (OSU) which identifies some of the low smoke standards used by industry.